Glass build platform is the way to go!

[curious aardvark]

the picture frame glass from pound/buck stores is 2mm thick.

actually I just measured it with the calipers. It's only 1.25 mm. Better heat transfer from the bed. And it's still pretty strong.
Just modelled a holder that will hold 7 sheets - assuming it prints !
But as it's a solid base I can use raft and that usually works okay

Now I just need to come up with a better way to attach the glass than bulldog clips as the heads always seem to hit the clips - no matter where I put them.

Also bought some vinyl based hairspray and a couple more sheets of glass.

I will try everything !